after upgrading to 14.04, Ruby was downgraded to 1.8.3 so I tried to upgrade using the following commands.

sudo apt-get install libgdbm-dev libncurses5-dev automake libtool bison libffi-dev

curl -L https://get.rvm.io | bash -s stable

source ~/.rvm/scripts/rvm

echo "source ~/.rvm/scripts/rvm" >> ~/.bashrc

rvm install 2.1.1

rvm use 2.1.1 --default

ruby -v

After that i ran

sudo gem install jekyll

It was installed sucessfully but, I am not able to use it is says

bash: /usr/local/bin/jekyll: /usr/bin/ruby1.9.1: bad interpreter: No such file or directory